JPS5897268A - Manufacture of electrode for battery - Google Patents

Abstract

PURPOSE:To increase the packed density of an electrode which is made by use of a three-dimensional net-like porous nickel base-plate, which contains almost spindle-shaped spherical spaces having a long diameter and a short diameter, by performing roll press several times in the direction perpendicular to said long diameter so as to gradually decrease the thickness of the electrode. CONSTITUTION:The figure represents a state in which an active material powder (nickel hydroxide in this case) (b) is packed into a base plate (a) having spindle- shaped spaces. The area represented by the symbol (c) principally consists of an aqueous solution, and is partially contaminated wh air. Roll press work was performed in up to 4 stages. Here, in carrying out roll press work in not less than two stages, the initial roll press was performed in such a manner that the thickness of the electrode became not less than 0.75mm.. As a result, it has been clarified that the packed density of the active material powder (b) becomes higher as roll press work is performed in more stages, and that such an effect becomes close to the maximum when roll press work is performed in 4 stages.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a battery electrode.

There are a wide variety of methods for manufacturing battery electrodes, but currently, industrially, there are two methods: ■Mainly press-molding active material powder and binder; ■Mainly molding a mixture of active material powder and binder with holes Method of applying to the core material or lattice of plates, screens, extracts, armholes, tometals, etc. (further pressurizing if necessary) ■ Filling a microporous metal tube or bag with active material powder Methods such as (1) filling an active material into a sintered substrate have been adopted. Among these methods, methods from (2) to (2) are more expensive, but the electrode strength is improved. - In the case of secondary batteries, method (1) or (2) is used in most cases, but in the case of secondary batteries, methods (2), (2), and (3), which are relatively robust, are used because they need to withstand repeated charging and discharging.

However, recently, three-dimensional network-like foam metal porous substrates have become commercially available, and their high porosity (approximately 95%) and relatively hard electronic conductivity make them possible to use as electrodes with high capacity and excellent properties. I have been considering gender. This substrate has a three-dimensional spread like a sintered substrate, but the pore diameter is much larger than that of a sintered substrate, and the pore size can be arbitrarily selected from 0.1 m to about 5 m, making it easy to use active material powder. Can be filled directly.

In other words, this can be said to be an intermediate manufacturing method between (1) and (2) above.

Electrodes using this substrate are relatively robust because they hold the active material powder inside a three-dimensional lattice, but they are more expensive than methods (1) and (2) above, so they are mainly used for secondary batteries. We have been considering it as an electrode. However, recently, they are being considered as electrodes for primary batteries, which require electrodes with high performance and take advantage of the advantage that the amount of active material can be controlled by the thickness of the substrate.

The present invention will be described in more detail regarding a method for manufacturing an electrode using this foamed metal porous substrate, and below, nickel hydroxide for a nickel positive electrode will be taken up as an example of active material powder.

As a result of various studies, the manufacturing process of this electrode is basically as follows:
An aqueous solution containing mainly nickel hydroxide powder is poured into the board by rubbing it into the substrate, and after removing the paste adhering to the surface of the board, it is placed between flat plates and pressurized, and then resin powder is applied. The method of reinforcing the electrode surface and cutting it last was superior in terms of uniform filling and simplicity. We also made suggestions regarding this process. However, in the flat plate pressurization process in the above process, even in the case of the two-kel positive electrode, a pressurizing force of approximately 500 to 9/cprW is required to obtain an active material packing density higher than that of the sintered nickel positive electrode.
In addition, powders such as cadmium oxide and lead oxide, which have a smaller particle size than nickel hydroxide, also require a pressing force of 4001 V/- or more, considering the current electrodes. In this case, after filling the paste with a sufficient liquid content, if the paste is immediately placed between the plates and pressurized, the substrate will have a three-dimensional lattice, so a two-dimensional screen or perforated plate will be created. Unlike when used as a core material, the powder and liquid in the paste cannot move quickly. For this reason, the lattice of the foamed metal tends to be cut by the pressure of the liquid containing the powder, and the electrode characteristics tend to deteriorate. Therefore, when pressing is performed by sandwiching the material between flat plates, it is necessary to apply pressure slowly or to reduce the liquid content (air escapes relatively quickly). In other words, when applying pressure between flat plates, the pressurizing machine itself requires a device with a large capacity, and it is also necessary to reduce the pressurizing speed and control the amount of liquid contained.

Therefore, we introduced a single-stage roll press to this pressurizing process, and found that as the electrode becomes thinner, the electrode begins to elongate in the direction of the roll press, and when the electrode is made even thinner, part of the electrode begins to elongate. Wavy or cracked. However, it was found that although this phenomenon occurs, there are differences in the changes in the shape of the spherical spaces in the porous metal foam.

In other words, depending on the deformation of the spherical space shape, the thinness of the electrode and the increase in active material packing density before the phenomenon is observed differ. Nickel hydroxide 80% in mixed powder mainly consisting of active material
wt%, nickel 16wt%, cobalt 4wt%
When the electrode thickness is filled in a foamed nickel substrate with a porosity of about 95 cm and a thickness of about 1.2 m11, the electrode thickness is converted into a packing density.If the spherical space shape is almost spherical, the packing density 420, mAh/cc or so,
If the spherical space shape is approximately spindle-shaped (having a major axis and a minor axis) and roll pressing is performed in the major axis direction, the packing density will similarly be 450 mAh/cc just before cracking occurs!
improved. Conversely, if roll press is performed in the short diameter direction, 3
The limit was 90 mAh/cc. 10 where the major axis is the minor axis
This value is obtained when it is about 5 times or more, but it slightly decreases when it is less than that. If there was a slight difference, cracks were less likely to occur, and the packing density was higher than in the spherical case. The reason for this is that in the case of roll pressing, the electrodes mainly expand in the roll pressing direction, but if the space is directional and has a substantially spindle shape, it is difficult to expand in the long axis direction.
This is thought to be due to the fact that the roll press allows for less stress to escape. However, when pressing between flat plates (800 to 9/ad), it is possible to achieve up to 50 tOraAh/ee, so it was not as high as that. The roll diameter of the roll press was 300 m, but even if the roll press was performed with various roll diameters and in the major axis direction, essentially 4
At a packing density of about 50 mAh/a6 or more, there was a tendency for some of the electrodes to become wavy or cracked.

However, by increasing the number of roll pressing steps (referred to as multi-stage roll pressing) and by increasing the diameter of the rolls used in the subsequent roll pressing, the packing density of the active material can be increased compared to performing roll pressing to the limit in one stage. Further improvement was achieved, and the desired value of 500 mAhAc could be obtained. In addition, in order to improve the discharge capacity density of the electrode after the pressurizing process as a power generation element when configuring the positive and negative electrode groups, flatness generally improves the discharge capacity density of the battery, but the multi-stage roll of the present invention In presses, it is better to have slight irregularities on the surface of the rolls used in at least the first roll press, which is more effective in dissipating the liquid in the paste and less deviations in the filling density and the filled active material. I was also able to find out.

The above effects will be explained using graphs. FIG. 1 shows a state in which a substrate a having a substantially spindle-shaped space is filled with active material powder (nickel hydroxide in this case) b. C is mainly an aqueous solution, with some air mixed in. Figure 2 shows the electrode plate (water content: about 30 wt/-!!-st) immediately after filling one layer of active material powder mainly composed of nickel hydroxide and removing the paste on the substrate surface. A roll press (using rolls with a diameter of 3005 m+) was carried out, and the thickness of the electrode plate was investigated at the time of filling just before the deformation of the electrode plate became uneven in each press. Roll pressing was performed up to four stages, and for two-stage roll pressing and above, the electrode thickness of the first stage of roll pressing was kept at 0.75 . As a result, it was found that the packing density of the roll press improved as the number of stages increased. It was also found that this effect is close to the maximum when using a three-stage roll press. Figure 3 shows the case where this three-stage roll press is used, and when pressing is performed using rolls of the same diameter (300 m11) (condition A), the first stage is 150 cm, 2
゜When the third stage has a roll diameter of 300 mm (condition B), the first stage has a roll diameter of 150 mm, the second stage has a roll diameter of 250 mm, and the third stage has a roll diameter of 3 mm.
Packing density of nickel hydroxide powder (,
) and the deviation amount C&') of the active material due to the pressing process relative to the amount of active material before the pressing process. In addition, in a three-stage roll press, the results are shown in (b) when unevenness is added to the surface of the first roll (the height difference between the uneven parts is approximately 01cm).
and (b'). For comparison, the same figure also shows the case where one-stage roll pressing (using rolls with flat surfaces) was carried out to its limit. As is clear from these results, as the roll diameter increases toward the later stages, the packing density improves.
Now possible up to mAh/cc. At this time, when the first stage roll was provided with irregularities, the packing density was further improved and the amount of active material powder deviated during the roll pressing process was reduced.

Such a phenomenon is hardly observed when the active material paste is applied to a planar core material (perforated plate, screen, extracted metal) and the roll pressing of the present invention is performed. Considering the reason for this, it can be inferred as follows. In other words, in the case of the present invention, a three-dimensional network-like foamed nickel porous material is used as a substitute for the core material, and it is filled with a paste of active material powder mainly composed of nickel hydroxide. The paste is less likely to move than if it was simply applied to a flat core material. However, the packing density was improved to about 500
Relatively strong pressure is required to increase it to mAh/cc. For this purpose, the strength is increased at once, and the more pressure is applied over a larger area, the more the active material is pulled out from within the substrate at once by the pressure of the paste, and the lattice of the substrate is cut. Therefore, electrodes with a bulk with a high liquid content have a small pressurizing surface, that is, a roll diameter is small, and the moisture in the gas (moisture) is the easiest to dissipate. It is thought that this is because removing (as is clear from the fact that only the It can also be inferred from the fact that if the roll surface is provided with irregularities to facilitate the movement of moisture, deviation of the solid portion will be reduced.

Example 1. Porosity 95%, thickness 1.20m, number of cells 5
0 pieces/inch, approximately spindle-shaped space with major axis/minor axis = 120, and 7-dihydroxide.

A mixture of 86 wt% Kel powder, 10 wt% Kel powder, and 4 wt% cobalt powder made into a paste with Q, 3 wt% carboxymethyl cellulose aqueous solution (water content: 3 Q wt%) After the surface is polished with a brush, pressure is applied between rolls having a diameter of 150 u. In this case, the roll surface is subjected to an end-processing process having concavities and convexities with a height difference of approximately 01 mm. Then, the electrode is pressed to reduce the thickness from 1.10 m to about 0.75 scales. Then, pressure is applied between rolls having a roll diameter of 2001111 to make the thickness about 0.70 scale. Subsequently, pressure was applied between rolls with a roll diameter of 30011Il, and the thickness was 0.6
Make it 51El. Next, this electrode plate is cut and immersed in a fluororesin suspension (concentration: 1 wt%) to form an electrode.

In Example 1, nickel hydroxide powder was used as the active material powder, but iron powder, zinc powder, lead oxide powder, cadmium oxide powder, silver oxide powder, manganese dioxide powder, etc. can also have similar effects. Particularly in the case of cadmium oxide powder having a small particle size, a roll diameter of 250 yen used in the final roll press during the pressing process of the present invention was sufficiently effective in improving the packing density.

The outline of the roll pressing process according to the present invention is shown in FIG. 4. In this figure, 1 indicates the electrode plate filled with paste, 2 indicates the first roll press process, and 3.4 indicates the second and third roll press processes, respectively. Reference numeral 5 denotes an auxiliary roller that can be moved up and down to adjust the speed between each roll pressing process. 1' is the electrode plate after completion of pressurization. The AA' cross section is a simplified sectional view of the surface of the roll 2, in which 6 shows a convex part, 7 shows a recessed part, and 8 shows the axis of the roll.

As described above, the roll pressing process according to the present invention is effective in improving the packing density of electrodes using a three-dimensional mesh foamed bilayer substrate, and the roll pressing process itself is suitable for continuous pressurization. It has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view of the electrode according to the present invention, Figure 2 is a diagram showing the relationship between the number of roll presses, hydration process, Kel packing density, and electrode thickness just before non-uniform deformation occurs. A diagram showing the relationship between three-stage roll press (when the roll diameter and the first stage roll surface are embossed), hydroxide processing, Kel packing density, and active material deviation amount during the roll press process,
FIG. 4 is a schematic diagram of the roll pressing process of the present invention and a schematic sectional view of the surface condition of Ronil used in the first stage roll pressing. a... Substrate, b... Active material powder, C... Aqueous solution or air, (a), (b)... Packing density of nickel hydroxide by three-roll press, (a'), (b)・・・
・Deviation rate (wt%) of active material powder by three-stage roll press
), 1, 1'... Electrode plate, 2.3.4... First stage, second stage, third stage roll press process, 5... Auxiliary roller, 6... Convexity on the roll surface. Part, 7... recessed part. Figure 1, &I L / Figure 2 IJL DoPL 3ku 4warm Figure 3

Claims (3)

[Claims] (1) In the process of filling a foamed metal porous substrate with a three-dimensional network structure with a paste-like mixture mainly composed of active material powder and press-molding it with a roll press, the foamed metal porous substrate has a continuous internal structure. The overlapping spherical space is approximately spindle-shaped with a major axis and a minor axis, most of which are parallel to one direction, and roll pressing is performed multiple times in a direction perpendicular to the major axis to sequentially thin the electrode. Characteristic manufacturing method for battery electrodes. (2) The diameter of the roll used for multiple roll presses is
Features 1. At least the previous process is smaller. Claims: - A method for manufacturing a battery electrode according to paragraph (1). (3) The method for manufacturing an electrode for a battery according to claim (1), wherein the surface of the roll used at least in the first stage in the plurality of roll pressing steps has an uneven surface.